Twenty-eight pediatric patients were treated with ceftriaxone (Ro 13-9904, CTRX) in the doses ranging from 8.75 to 25 mg/kg every 12 hours for 3.5 to 11.5 days, and the clinical efficacy and side effects were evaluated. Among the 21 children with bacterial infections including pneumonia, acute bronchitis, otitis media, tonsillitis and urinary tract infections, the results were excellent in 9, good in 11, and fair in 1 patient. Out of the 28 patients, 2 patients had diarrhea, 3 patients had slightly elevated serum concentrations of transaminases, and 2 patients showed eosinophilia. The serum concentrations of CTRX in 5 children ranged from 50.0 to 93.8 micrograms/ml (mean 75.0 micrograms/ml) at 15 minutes and from 10.2 to 15.6 micrograms/ml (mean 13.4 micrograms/ml at 6 hours after 10 mg/kg intravenous bolus injection of CTRX. The serum half-lives were from 2.61 to 8.30 hours (mean 6.16 hours), and urinary recovery rates were from 43.3 to 58.0% (mean 48.5%) during 0-6 hours and from 52.0 to 66.1% (mean 59.4%) during 0-12 hours. After 20 mg/kg intravenous bolus injection of CTRX in 4 children, the serum concentrations of CTRX were from 118.8 to 162.5 micrograms/ml (mean 139.1 micrograms/ml) at 15 minutes and from 18.0 to 21.1 micrograms/ml (mean 19.2 micrograms/ml) at 6 hours. The serum half-lives were 4.07 to 6.34 hours (mean 5.13 hours), and urinary recovery rates were 38.6 to 51.1% (mean 45.4%) during 0-6 hours and from 54.8 to 64.0% (mean 59.0%) during 0-12 hours. Patients with impairment of renal function were excluded from this pharmacokinetic study.